In the last decade or so, energy concerns have resulted in a trend toward the use of smaller engines, both diesel and spark ignition in vehicles of various types. The use of such smaller engines has resulted lower fuel consumption because of the smaller size of the engine as well as an improvement in fuel economy due to the resulting lesser vehicle weight.
At the same time, there has been an existing concern to improve the power output of the smaller engines. This, in turn, has resulted in resort to various types of energy recapture devices such as turbochargers which recapture part of the energy of the exhaust stream from a typical internal combustion engine and utilize it to increase the combustion air charge to the engine by compressing the air. While turbochargers work well for their intended purpose, in the process of compressing air, they raise the temperature thereof, thereby decreasing the density of such air, and thereby decreasing the molecular volume of oxygen fed to an engine in a given volume of air over that that would be present had the air not been heated.
This phenomena has been recognized and as a consequence, there has been increasing resort to the use of so-caller intercoolers or charge air coolers. Such coolers are heat exchangers that are placed between the outlet compressed air stream of a turbocharger and the input air stream to the internal combustion engine. By cooling the air stream after turbocharging and before it is fed to the internal combustion engine, the combustion air stream is densified with the consequence that a larger number of oxygen molecules per a given volume of air to the internal combustion engine is present. This in turn allows a larger quantity of fuel to be combusted, which, in turn, means that the output power of the engine will be increased because of the greater power available from the proper stoichiometric consumption of a greater quantity of fuel. Further, in the case of diesel engines, the use of an intercooler reduces particulate emissions.
Because charge air coolers are invariably utilized in an air to air heat exchange environment, one heat exchange fluid path (that through which the combustion air flows) must be relatively large (as, for example, compared to tubing used in vehicular radiators) so as to not unduly impede the flow of combustion air to the engine. At the same time, because weight is always a concern in the design of vehicles, it is highly desirable that the charge air cooler have a minimum weight.
As a consequence, it is highly desirable that the conduits or tubes through which the charge air flows be sufficiently large as to not impede air flow while at the same time, it is desirable that such tubes have a wall thickness as thin as possible so as to minimize the weight of the charge air cooler.
This in turn has suggested that tubes formed by extrusion processes not be used since it is impossible, or at the least, undesirably expensive to form tubes sufficiently large as to be suitable in charge air cooler applications with sufficiently thin sidewalls as to minimize both weight and material expense.
As a consequence, there have been proposals of fabricated tubes for charge air coolers made of multiple pieces. One such proposal is illustrated in U.S. Pat. No. 4,501,321 issued Feb. 26, 1985 to Real et al. In this patent, tubes are formed by utilizing inner and outer channel members each having a bottom wall and two transfer side edges. A turbulator is fitted between the channels and the channels are formed such that frictional contact between the legs of opposing channels tends to hold the tube in assembly prior to a metallurgical bonding process.
Further, the Real assembly is touted as being an adjustable one whereby the cross-sectional area (in terms of the width) may be varied to receive various sizes of turbulators.
As a practical matter, the Real solution is not altogether satisfactory. Because only frictional contact between legs of the channel exist to hold the assembly together, positive contact between various parts of the turbulator and the bases of the two channels cannot be guaranteed. Thus, heat exchange to the exterior of each tube via the turbulator or internal fin cannot be guaranteed because the possibility of air gaps between the turbulator and base of the associated channel is not precluded. Thus, while Real provides an efficiently manufactured tube construction, its efficiency in a heat exchanger such as a charge air cooler is not as great as might be desired.
The present invention is directed to overcoming one or more of the above problems.